This invention relates to methods and apparatuses for impregnating a fibrous web with a liquid.
Many processes involve impregnating an absorbent web with a liquid. Among these is a process for manufacturing plastic pipe that includes a resin impregnated fibrous material as the inner layer to provide corrosion resistance in severe operating conditions. For example, a layer of resin impregnated glass fiber mat is used as the liner for reinforced epoxy pipe in severe chemical service such as transporting caustic solutions at elevated temperatures.
A common problem in making plastic pipe containing a layer of resin impregnated fibrous material is how to saturate the material quickly and completely with the liquid resin. If the fibrous material is not completely saturated with resin, residual air results in voids after curing which can lead to failure from chemical attack of the body of the pipe.
One method used to saturate the fibrous material is to first wind the material around a rotating mandrel, and then squeegee resin into the liner material. However, this method is messy and time consuming since two separate steps are required, namely, a winding step and a resin-impregnating step. In addition, results are too variable since the process is entirely manual.
Another method commonly used to saturate the fibrous material is to soak the material in resin before it is wound around the mandrel. However, this method cannot be used with all types of fibrous materials because in some resin/web combinations the resin dissolves the binder holding the liner material together.
A third method is to pour resin onto the fibrous material immediately in front of the pinch point where the material first contacts the mandrel. The pressure exerted by the mandrel on the fibrous material tends to force the resin into the material. Although this method is useful in some applications, it has disadvantages. For example, when a thick or dense web is used, or the liquid is highly viscous, complete impregnation can be achieved only at slow, uneconomical speeds.
Therefore, there is a need for a high speed, dependable, and economical method and apparatus for saturating a web containing fibrous material with liquid resin.